Marek Stibal

Microbial Communities on Glacier Surfaces in Svalbard: Impact of Physical and Chemical Properties on Abundance and Structure of Cyanobacteria and Algae

Microbial communities occurring in three types of supraglacial habitats—cryoconite holes, medial moraines, and supraglacial kames—at several glaciers in the Arctic archipelago of Svalbard were investigated. Abundance, biovolume, and community structure were evaluated by using epifluorescence microscopy and culturing methods. Particular emphasis was laid on distinctions in the chemical and physical properties of the supraglacial habitats and their relation to the microbial communities, and quantitative multivariate analyses were used to assess potential relationships. Varying pH (4.8 in cryoconite; 8.5 in a moraine) and texture (the proportion of coarse fraction 2% of dry weight in cryoconite; 99% dw in a kame) were found, and rather low concentrations of organic matter (0.3% of dry weight in a kame; 22% dw in cryoconite) and nutrients (nitrogen up to 0.4% dw, phosphorus up to 0.8% dw) were determined in the samples. In cryoconite sediment, the highest numbers of bacteria, cyanobacteria, and algae were found, whereas relatively low microbial abundances were recorded in moraines and kames. Cyanobacterial cells were significantly more abundant than microalgal ones in cryoconite and supraglacial kames. Different species of the cyanobacterial genus Leptolyngbya were by far the most represented in all samples, and cyanobacteria of the genera Phormidium and Nostoc prevailed in cultures isolated from cryoconite samples. These species are considered opportunistic organisms with wide ecological valency and strong colonizing potential rather than glacial specialists. Statistical analyses suggest that fine sediment with higher water content is the most suitable condition for bacteria, cyanobacteria, and algae. Also, a positive impact of lower pH on microbial growth was found. The fate of a microbial cell deposited on the glacier surface seems therefore predetermined by the physical and chemical factors such as texture of sediment and water content rather than spatial factors or the origin of sediment.

Microbial primary production on an Arctic glacier is insignificant in comparison with allochthonous organic carbon input

Cryoconite holes are unique freshwater environments on glacier surfaces, formed when solar-heated dark debris melts down into the ice. Active photoautotrophic microorganisms are abundant within the holes and fix inorganic carbon due to the availability of liquid water and solar radiation. Cryoconite holes are potentially important sources of organic carbon to the glacial ecosystem, but the relative magnitudes of autochthonous microbial primary production and wind-borne allochthonous organic matter brought are unknown. Here, we compare an estimate of annual microbial primary production in 2006 on Werenskioldbreen, a Svalbard glacier, with the organic carbon content of cryoconite debris. There is a great disparity between annual primary production (4.3 mug C g(-1) year(-1)) and the high content of organic carbon within the debris (1.7-4.5%, equivalent to 8500-22 000 mug C g(-1) debris). Long-term accumulation of autochthonous organic matter is considered unlikely due to ablation dynamics and the surface hydrology of the glacier. Rather, it is more likely that the majority of the organic matter on Werenskioldbreen is allochthonous. Hence, although glacier surfaces can be a significant source of organic carbon for glacial environments on Svalbard, they may be reservoirs rather than oases of high productivity.

Photophysiology and albedo-changing potential of the ice algal community on the surface of the Greenland ice sheet

Darkening of parts of the Greenland ice sheet surface during the summer months leads to reduced albedo and increased melting. Here we show that heavily pigmented, actively photosynthesising microalgae and cyanobacteria are present on the bare ice. We demonstrate the widespread abundance of green algae in the Zygnematophyceae on the ice sheet surface in Southwest Greenland. Photophysiological measurements (variable chlorophyll fluorescence) indicate that the ice algae likely use screening mechanisms to downregulate photosynthesis when exposed to high intensities of visible and ultraviolet radiation, rather than non-photochemical quenching or cell movement. Using imaging microspectrophotometry, we demonstrate that intact cells and filaments absorb light with characteristic spectral profiles across ultraviolet and visible wavelengths, whereas inorganic dust particles typical for these areas display little absorption. Our results indicate that the phototrophic community growing directly on the bare ice, through their photophysiology, most likely have an important role in changing albedo, and subsequently may impact melt rates on the ice sheet.

Organic matter content and quality in supraglacial debris across the ablation zone of the Greenland ice sheet

Abstract Quantifying the biogeochemical cycling of carbon in glacial ecosystems is of great significance for regional, and potentially global, carbon flow estimations. The concentration and quality of organic carbon (OC) is an important indicator of biogeochemical and physical processes that prevail in an ice-sheet ecosystem. Here we determine the content and quality of OC in debris from the surface of the Greenland ice sheet (GrIS) using microscopic, chromatographic, spectrophotometric and high-temperature combustion techniques. The total OC content in the debris increased with distance from the edge of the ice sheet, from virtually zero to >6% dry weight at 50 km inland, and there was a peak in the carbohydrate proportion and the microbial abundance at ∼6km inland. The highest (galactose + mannose)/(arabinose + xylose) ratios, indicating maximum autochthonous microbial production, were found at >10km inland. We propose that three key processes influence the carbon cycling on the GrIS: aeolian input of microbial inoculum and nutrients, in situ biological C transformation and the wash-away of supraglacial debris by meltwaters. We show that all these processes have significant spatial variability. While the total OC content of the debris on the ice sheet is probably controlled by the physical processes of wind transport and wash-away by meltwater, the microbial abundance and the quantity of the labile cell-contained OC within the debris is likely to be driven by the balance between the wash-away and the microbial productivity.

Morphological variability in selected heterocystous cyanobacterial strains as a response to varied temperature, light intensity and medium composition.

The effect of temperature, light and nutrient composition on morphological traits was determined in seven nostocacean cyanobacteria (Anabaena planctonica, A. sphaerica var. conoidea, A. spiroides, Aphanizomenon gracile, Nostoc sp., Scytonema sp., and Tolypothrix sp.). Their morphological variability was high but only some of the features showed changes reflecting varied growth conditions. The frequency of heterocyst occurrence decreased with increasing nitrogen concentration. Within the range studied, the effect of temperature on heterocyst frequency of Tolypothrix sp. and planktonic Anabaena strains could be fitted by a normal curve with a clear optimum while linear correlation was found in Aphanizomenon gracile. T-and S-type branching was observed in both Scytonema sp. and Tolypothrix sp. strains. T-type branching was found to be markedly dependent on nitrogen concentration. The abundance of necridic cells of Tolypothrix sp. increased linearly with temperature and light intensity. Regularity of trichome coiling of A. spiroides depended on culture medium, suggesting that nutrient composition may be the main controlling factor. In contrast, the effect of the experimental conditions on the dimensions of vegetative cells and heterocysts was weak. Their variability was markedly higher within each experimental treatment than between treatments.